In recent years, attention has been given to display devices in which a touch detection device referred to as a so-called touch panel is provided on a display device such as a liquid crystal display device, or a touch panel and a display device are integrated into a single unit, and the display device is made to display various button images to enable information to be input without ordinary real buttons. Such display devices having a touch detection function do not need input devices such as a keyboard, a mouse and a keypad, and thus tend to be broadly used as display devices of computers, portable information terminals such as cell phones, etc.
As such a touch panel, a capacitive touch panel is known in which plural electrodes extending in a direction are arranged to intersect plural electrodes extending in another direction. In this type of touch panel, the electrodes are connected to a control circuit, and are supplied by the control circuit with an excitation current to detect closely situated external object.
As a display device having a touch detection function, a so-called in-cell touch panel is proposed in addition to a so-called on-cell display device in which a touch panel is provided on a display surface of the display device. In the in-cell display device, common electrodes for display, which are originally provided in the display device, are also used as one of a pair of groups of electrodes for a touch sensor, and the other group of electrodes is provided to intersect the common electrodes.
Furthermore, as a mode for detecting a touch position, a mutual detection mode and a self-detection mode are known. In the mutual detection mode, an AC drive signal is supplied to one of a pair of groups of electrodes, and detection signals generated at the other group of electrodes are processed, to thereby detect a touch position. In the self-detection mode, an AC drive signal is supplied to one of a pair of groups of electrodes, and a signal generated to the above one of the pair of groups of electrodes is processed, thereby detecting a touch position.
It should be noted that in the in-cell display device having a touch detection function, each frame time period is divided into a time period in which an image is displayed (image display time period) and a time period in which a touch position is detected (touch detection period). Because of such a technical feature, in recent years, in the case where display devices are made to have a larger size and a higher definition, and their touch panels are made to have a higher resolution, there is a risk that the following problems will arise:
(1) As the touch detection period increases, the display time period decreases. Inevitably, the display quality is reduced. Also, as a touch drive frequency increases, the power consumption of the display device having a touch detection function increases.
(2) If the amount of touch data to be processed increases, there is a case where a delay is caused in touch data processing including a touch data transfer. Also, as the number of touch sensors increases, the power consumption of the display device having a touch detection function increases.